- Discourse on the Method of Rightly Conducting One’s Reason and of Seeking Truth in the Sciences (French: Discours de la Méthode pour bien conduire sa raison, et chercher la vérité dans les sciences) is a philosophical and autobiographical treatise published by René Descartes in 1637. It is best known as the source of the famous quotation “Je pense, donc je suis” (“I think, therefore I am”, or “I am thinking, therefore I exist”), which occurs in Part IV of the work. A similar argument, without this precise wording, is found in Meditations on First Philosophy (1641), and a Latin version of the same statement Cogito, ergo sum is found in Principles of Philosophy (1644).